During the drilling of petroleum related wells the drill string is occasionally removed from the well bore, and re-installed in the well bore. That activity is referred to as tripping the string. It is effectively a round trip. Drilling floor activity is a dangerous process and most injuries occur during the tripping activity.
Considerable effort has been made to mechanize the tripping process. Part of the effort has been directed to separating the drill string from operating personnel. The drill pipe is normally broken into stands of two or three joints each and racked, standing on end, in the drilling rig at two areas of the drilling floor. On most large drilling rigs, a bridge crane type racking system, incorporating a hoist, moves horizontally in two mutually perpendicular directions to positively position the upper end of a stand being racked. The lower end of the stand, however, tends to swing and movement of the upper end only slowly controls the lower end. It tends to swing about. Drilling floor personnel normally control the lower end until it is properly placed in the racking area. That personal contact, all too often results in injuries.
Efforts to reduce human contact with the lower end of a pipe stand, have brought manipulators into practice to position the lower end of the stand being moved to racks. The manipulators are powered and operated somewhat like a back hoe. They reach in from the side of the drilling floor, grasp the lower end of the stand, and move it to the desired position. They are powered and effective but they are costly, take up needed space, and they are manned. The man is still at risk.
With the drill racking in progress, the drilling floor becomes crowded. Drill string manipulation machines do not have an open area in which to function. Power tongs have to operate in the area that would be needed for some forms of pipe manipulation machines.
There is a need for controllable drill pipe racking aids that do not stand on the drilling floor. When the drill pipe is in the well bore, and drilling activity is underway, it is advantageous to remove the racking aids from the area they necessarily occupy during tripping. The present invention addresses that problem.
The upper end of the racks of drill pipe stands have customarily been organized and controlled by combs that separate the individual banks of standing drill pipe. They have worked quite well in the past. Such combs should work well to organize and control the lower ends in a similar fashion. The control of the upper ends of pipe will not insert the lower end of the pipe in the combs because of the pendulum swing common to the lower end. Any racking aid has to aid the swinging pipe in finding the proper route into the lower combs. If lower combs are used they have to have special features not required of the upper combs. Such features are disclosed herein.